Electrical conductors and methods of manufacture thereof



Dec. 11, 1962 J. P. KELLEY, JR 3,067,569

ELECTRICAL CONDUCTORS AND METHODS OF MANUFACTURE THEREOF Filed Feb. 28, 1957 IO I3 FIG. I 1;

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I N VEN TOR. 5 JOHN P KELL EY JR. 2,?

ATTORNEYS United States Patent Oflfice 3,067,569 Patented Dec. 11, 1962 ELECTRICAL CONDUCTSRS AND METHQDS @F MANUFACTURE THEREOF John P. Kelley, Jra, Framingharn, Mass, assignor, by mesne assignments, to The Dow Chemical Company,

Midland, Mich, a corporation of Delaware Filed Feb. 28, 1957, Ser. No. 643,083 11 Claims. (Cl. 57-139) This invention relates to improvements in electrical conductors and, more particularly to electrical conductors having high flexibility and resistance to bending fatigue, light weight, small volume, low electrical resistance and relatively high tensile strength and to the method of using film and foil in making such conductors.

In many applications, but especially for use in electrical cords for various types of appliances, there is and has been a great demand for electrical conductors combining the characteristic of great flexibility and resistance to bending fatigue, such as, for example, cords for electric irons, shavers, toasters, tools, telephone hand sets, and the like, where an essential purpose and function of the appliance resides in its portability while connected to a source of electric power for the actuating element with in the appliance. Heretofore the actual electrical conductor material in such cords has been a plurality of very fine, loosely twisted or braided copper Wires, referred to generally in the trade as tinsel. While such tinsel provided the desired flexibility and low resistance, it had extremely low tensile strength and relatively poor resistance to flexing fatigue. When surrounded with suitable textile or fibrous yarn or wrapping to provide adequate tensile strength as well as insulation, the resultant insulated conductor lost considerable of the desired flexibility and became quite heavy and bulky. Further, such fibrous filler material and the loosely twisted or braided tinsel had the undesirable property of being relatively hygroscopic. The weak tinsel was not only relatively expensive and troublesome to handle in manufacture, but its Weakness required that it be loosely twisted or braided and, thus, that the conductor be relatively voluminous.

It is an object of this invention to provide a conductor or conductor material which is far more flexible and has far greater tensile strength than the tinsel available heretofore. Another object and advantage of this invention is that the material may be tightly braided or twisted and thus may be very compact while providing a much higher ratio of conductive surface to Weight of conductor than available in the prior art tinsel. Conductors made according to this invention are much less expensive to produce and are easily handled in conventional conductorproducing machinery. It may be highly non-hygroscopic. It may be readily combined with dense, high tensile reinforcing textile threads or cords.

Other and further objects and advantages of this invention will be apparent from the following specification, claims, and drawings, in which:

FIG. 1 is a greatly enlarged cross section (taken along the line 1-1 of FIG. 2) of an elemental conductor filament made according to this invention.

FIG. 2 is a plan view, partly broken away, of the conductor filament shown in FIG. 1.

FIG. 3 is a broken-away elevation of an insulated and twisted cabled conductor embodying this invention.

FIG. 4 is a detail of a modification of the conductor shown in FIG. 3.

FIG. 5 is a detail of a still further modified conductor.

In general, the conductor material embodying this invention is produced by laminating relatively wide webs of a foil of a conductive metal, such as aluminum, copper, silver, or the like to a relatively high strength film, such as tensioned polyethylene terephthalate (Mylar, E. I. du Pont de Nemours Companys registered trademark for their type of polyester film), polystyrene, cellulose acetate-butyrate, plasticized polyvinyl chloride, chlorinated polyvinylidene (sarau), and the like. Any suitable laminating adhesive may be used, such as a lacquer type comprising a natural and/ or synthetic resin dissolved in volatile solvent therefor, or a suitable thermoplastic resin, such as polyethylene. If, as in the case of polyethylene terephthalate film, it may be desirable to take measures to inhibit delamination. The substrate film is preferably laminated on both sides to a conductive foil, although in some applications, a single lamina of toll on one face may be desired.

After the web of film and foil is so laminated, it is slit lengthwise into long filaments or ribbons of the desired widths in standard slitting equipment, such as may be used in slitting such laminae into yarns or ribbons of the type shown in the US. patent to Prindle, No. 2,714,569, or Lacy, No. 2,772,994. The elemental filaments so produced are usually spooled for use in standard cable or braiding equipment to produce a twisted or braided conductor, except that this equipment may be set to produce a tightly braided or twisted conductor. The filaments may be twisted or braided upon themselves or, for greater tensile strength, about a central core of low-stretch nylon, polyester filament (Dacron, a registered trademark of E. I. du Pont de Nemours Company for polyester textiles), resinated cotton or rayon, high tensile cellulose acetate, or similar high-tensile, low-stretch cords such as are commonly used for tire fabrics in the tire industry.

The conductors so produced may then be covered or wound with any suitable dielectric material, such as extruded polyethylene, cellulose acetate-butyrate, rubber and rubber compounds, textile or paper looms, or similar conductor cord insulation as is conventionally employed, except, of course, that such covering may be designed more for its dielectric properties rather than tensile strength. To prevent the desirable flexibility of a conductor embodying the invention from being diminished, any reinforcing or covering is generally minimized in bulk to prevent such bulk from detracting from flexibility.

A specific example of a conductor made according to this invention is as shown in the accompanying drawings and was produced as follows:

A base film ill, of tensioned polyethylene terephthalate .001 inch thick, was laminated on both sides with aluminum foil 33;, .00035 inch thick. A polyethylene thermoplastic resin 12 was the adhesive, the adhesive being bonded to the film and being applied in no greater thickness than was necessary to bond the foil to the film. The web of laminated film and foil was slit to filaments one-fiftieth of an inch thick, providing a conducting filament it having cross-sectional dimensions of approximately .00 x .02".

The above-described conductive filament was suitably spooled from the slitting machine and such spooled filaments were then twisted in a conventional spinning machine as follows: Three filaments 10 were thrown and twisted, three turns per inch, to form a tightly twisted cord 20. Two cords 20 were then twisted together, with three turns per inch, to form a strand 30. Three strands 30 Were then twisted together, three turns per inch, ,to form a cabled conductor 40, consisting of eighteen ends or filaments 10.

The highly flexible conductor 4-0 was tested and found to have a tensile strength of 17 pounds and an electrical resistance of .073 ohm per foot; it withstood cycles in an Underwriters Laboratory film tester used to test heater cords.

oneness To complete the conductor id for use as a flexible electrical appliance cord 60, two such conductors were covered with extruded plastic 50.

It should be clear that, without de arting from the scope of this invention, which comprises the desirable high-tensile strength and flexibility of the non-conductive base film 11 and the desirable high ratio of conductive surface to weight of the weak and brittle conductive metal foil 13 to produce the conductor filament it which enhances the desirable characteristics of both components, conductors made of filament are not confined in struc ture to the specific example 4i? shown in the drawings. Thus, instead of being of twisted cabled construction, the conductor 40 might have been braided from filaments, cords or strands. Further, such filaments, cords or strands may be braided or twisted with, about, and/or within filaments, yarns or strands of low-stretch reinforcement materials which further increase tensile strength. For example, FIG. 4 shows a modification of the cable conductor as shown in FIG. 3, in which modification the strands 13d of the cable 145i (instead of eing twisted only upon themselves, as the strands 3d of the cable 49 shown in FIG. 3) are twisted about a central core of a high-tensile, low-stretch cord 131. Similarly, filaments 210 may be braided about a central reinforcing cord 231 to form a conductor cord 2%, as shown in PEG. 5. in the appended claims, the verb entwine, as it may be applied in its various forms to a plurality of filaments, is to be understood to encompass any serving of a pin- Iality of filaments, helically and/ or linearly about an axis as well as twisting, braiding, or otherwise throwing, spinning or weaving the filaments. At the outset, it was mentioned that the foil 13 may be laminated on only one side of the film 11; this is desirable where the filament is intended for use in braided tubular shields, as, for example, in co-axial lead-in cables for radio frequency conductors, as the grounding conductor in a power cord, as a wave guide or wherever else it may be desired to employ a conductor which is conductive on one surface but not the other. Nor is the conductive filament limited to a three-layer sandwich, as shown in the drawings; depending upon the particular requirements, any number of laminae of film and rfoil may be employed.

The particular adhesive employed for lamination was uncolored. In many applications a suitable dye or pigment may be incorporated in the adhesive or the film to provide an inherent color coding of the actual conductor filaments in addition to the usual color coding of an overlying insulation.

The single filament may be employed as a conductor without combination with other filaments as. for example, for very low amperage radio frequency currents. In such instances, a greater factor of safety for tensile strength is usually allowed. The synergistic effect of a plurality of conductive filaments made according to this invention may be due to the contact between the conductive surfaces of the foil in the individual filaments. That is, if in any one foil surface there may be a break due to fracture or a reduction due to a pin-hole in the foil, such break or pin-hole will be bridged by the contacting conductive surface of an adjacent filament.

It is to be understood that the term foil as used in the foregoing specification and following claims is to be understood to include vapor-deposited or plated metallic films, as well as rolled or beaten metallic foils. This invention, therefore, is not to be limited to the specific embodiments and variations disclosed, but only by the appended claims.

What is claimed is:

1. An uncoated filament for electrical conductors comprising a slit laminate of metallic foil and a non-fibrous organic film bonded thereto, said film having greater tensile strength and resistance to bending fatigue than said foil, said foil providing an electrically conductive outer surface on said filament.

2. A filament for electrical conductors as defined in claim 1 in which said foil is of the class consisting of silver, copper, and aluminum foil and said foil constitutes laminae on opposite surfaces of said film.

3. An electrical conductor comprising a plurality of entwined filaments in which an individual filament of the plurality comprises a laminate of a metallic foil of the class of metals consisting of silver, copper, and aluminum and a non-fibrous organic film, said foil being bonded to opposite surfaces of said film to provide electrically conductive surfaces on said filament and said film having a greater tensile strength and resistance to bending fatigue than said foil.

4. An electrical conductor as defined in claim 3 in which the film of the filaments is of the class consisting of polyester, plasticized polyvinyl chloride, chlorinated polyvinylidene, polystyrene, and cellulosic films and said filaments are twisted together.

5. An electrical conductor as defined in claim 3 in which the film of the filaments is of the class consisting of polyester, plasticized polyvinyl chloride, chlorinated polyvinylidene, polystyrene, and cellulosic films and said filaments are braided together.

6. An electrical conductor as defined in claim 3 in which said filaments are entwined with a relatively hightensile, low-stretch textile supporting strand.

7. The method of making conductive filaments for electrical conductors comprising the steps of laminating a web of conductive metallic foil to a web of organic non- ;fiorous film to form a laminate with an electrically conductive outer surface, said film having a greater tensile strength and resistance to bending fatigue than said foil, and then slitting the laminate into filaments.

S. The method of making electrical conductors comprising the steps of laminating a web of conductive metallic foil to the opposite surfaces of an organic non-fibrous film having a greater tensile strength and resistance to bending fatigue than said foil to provide a laminated web with electrically conductive outer surfaces, slitting said laminate into filaments, and then entwining said filaments to bring conductive surfaces of separate filaments into contact with each other.

9. The method as defined in claim 8 including the step of entwining said filaments with a reinforcing textile cord.

10. The method as defined in claim 9 in which the step of entwining comprises twisting said filaments.

ll. The method as defined in claim 9 in which the step of entwining comprises braiding said filaments.

References Cited in the file of this patent UNITED STATES PATENTS 1,773,580 Franke Aug. 19, 1930 1,983,520 Charch et al Dec. 11, 1934 2,027,296 Stuart et al. Jan. 7, 1936 2,569,764 Jonas Oct. 2, 1951 2,609,417 Cox et al. Sept. 2, 1952 2,631,219 Suchy Mar. 10, 1953 2,740,732 Peck et al. Apr. 3, 1956 2,772,994 Lacy Dec. 4, 1956 FOREIGN PATElJTS 686,031 Great Britain Jan. 14, 1953 

1. AN UNCOATED FILAMENT FOR ELECTRICAL CONDUCTORS COMPRISING A SLIT LAMINATE OF METALLIC FOIL AND NON-FIBROUS ORGANIC FILM BONDED THERETO, SAID FILM HAVING GREATER TENSILE STRENGTH AND RESISTANCE TO BENDING FATIGUE THAN SAID FOIL, SAID FOIL PROVIDING AN ELECTRICALLY CONDUCTIVE OUTER SURFACE ON SAID FILAMENT.
 7. THE METHOD OF MAKING CONDUCTIVE FILAMENTS FOR ELECTRICAL CONDUCTORS COMPRISING THE STEPS OF LAMINATING A WEB OF CONDUCTIVE METALLIC FOIL TO A WEB OF ORGANIC NONFIBROUS FILM TO FORM A LAMINATE WITH AN ELECTRICALLY CONDUCTIVE OUTER SURFACE, SAID FILM HAVING A GREATER TENSILE STRENGTH SAID RESISTANCE TO BENDING FATIGUE THAN SAID FOIL, AND THEN SLITTING THE LAMINATE INTO FILAMENTS. 